The invention relates to a suppression device for an electronic appliance having a plug-in device which has at least one plug-in element and is designed for attachment to a housing of the electronic appliance, with a capacitor being provided in order to improve the electromagnetic sensitivity.
In order to ensure correct operation of electronic devices, these devices must be shielded against interference radiation which occurs in particular in the radio-frequency band. Such suppression measures are normally carried out on a printed circuit board which is located in the interior of the electronic appliance.
DE 33 26 629 C2 discloses an interference protection filter for electronic controllers in a motor vehicle, in which the interference protection filter is arranged directly adjacent to the input of the plug connections in the housing. A capacitively acting switching element in this case has two capacitor plates, with one capacitor plate being in the form of a line which leads to the electronic circuit from that end of a connector which projects into the electronic appliance.
This has the disadvantage that this suppression device can only attenuate interference radiation, since the supply line which is connected to the suppression device still radiates power, and this has a negative effect on the electronic components.
Standard bushing capacitors which are normally used for suppression and are soldered into metal housings are expensive and complex to process.
The invention is thus based on the object of specifying a simple and low-cost suppression measure for electronic appliances which are also suitable for mass production.
According to the invention, the object is achieved in that the capacitor is arranged outside the housing of the electronic appliance and is electrically connected firstly to a plug-in element of the plug-in device and secondly to the potential of the electrically conductive housing.
The invention has the advantage that the suppression is actually provided on the outside of the electronic appliance, and interference radiation cannot enter the housing interior at all. Such a suppression device is simple to install since the insertion of the connector into the housing produces a suppression filter. There are no additional installation measures.
In order to make it possible to dispense with cables to the capacitor, a first capacitor plate is formed in or on the plug-in device.
The first capacitor plate is advantageously formed from the plug-in element itself. This can easily be achieved, for example, by upsetting the connector pin. This further simplifies the production of the connector.
Alternatively, the first capacitor plate is formed by a conductor surface which is arranged on a mounting element, is arranged alongside the plug-in element and is electrically connected to it. This is done simply by the first capacitor surface enclosing the plug-in element, which has no insulation and carries an electrical potential, in an interlocking and/or force-fitting manner. This results in a device which can be handled particularly well for mass production.
The mounting element advantageously has at least one further conductor surface, which forms the second capacitor plate and is arranged above and/or underneath the first conductor surface, electrically isolated from it. The mounting element together with the two capacitor plates can be prefabricated, so that only the electrical connection still needs to be produced during connector installation.
In a development of the invention, a conductor surface which forms the second capacitor plate is in the form of a contact coating on one surface of the mounting element. In this case, there are two possible ways to produce the electrical connection for the housing potential.
Firstly, the electrically conductive contact coating of the mounting element is located directly on the outside of the housing, resulting in a conductive connection and in the contact coating assuming the housing potential. In this arrangement, there is no need whatsoever for any additional conductive connections.
The contact coating is advantageously in the form of a conductive adhesive, so that the mounting element is at the same time attached to the housing.
In another refinement, the electrical connection between that conductor surface of the mounting element which forms the second capacitor plate and the housing is produced by means of at least one attachment element which holds the mounting element and/or the plug-in device on the housing.
The housing potential is in this case produced via a screw, riveted or press-in connections, which are present in any case, at at least one point.
If the second conductor surface is in the form of a contact surface, insulation is arranged between it and the outside of the housing. In this case as well, the plug-in device is located in an unchanged manner and firmly on the housing outer wall.
In order to form a further capacitor for the same plug-in element, the mounting element has two further conductor surfaces, which are located one above the other and are electrically isolated from one another, with the third conductor surface being electrically connected to the plug-in element and the fourth conductor surface being electrically connected to the housing potential. This multilayer construction allows larger capacitance values to be achieved for each connector pin.
In one simple refinement, the plug-in device has a number of plug-in elements, with the first capacitor surfaces, which are electrically isolated from one another and are associated with different plug-in elements, being formed in a conductor coating.
The second capacitor surface is formed by the unstructured contact coating for all the plug-in elements. An arrangement such as this can easily be produced by means of film printed circuits.
In one advantageous development, the mounting element can be fitted on that side of the plug-in device which faces the housing and can be made contact with in that a first capacitor surface in each case encloses in each case one plug-in element.
A commercially available connector can thus be provided with an additional suppression device according to the invention.